Comment by throwaway82003

In some phones, if you enable 'show system apps', you can see the following fb apps:

Facebook App Installer

Facebook App Manager

Facebook Services

All 3 can be disabled.

Also they usually have Instagram and fb messenger pre-installed.

Also many apps come with fb SDK. On android, the app 'ClassyShark3xodus' can be used to check it. Available on Fdroid.